1. Field of the Invention
The present invention relates to a process for the shaping of filamentary structures of polyvinyl alcohol (hereinafter "PVA"), and, more especially, relates to a process for the shaping of filamentary structures of PVA useful in the manufacture of certain synthetic paper products.
2. Description of the Prior Art
The art is of course replete with various methods for the shaping of various filamentary and fibrous structures from both the natural and the synthetic resins. Such processes include both the normal wet, dry and melt spinning, as well as other methods such as fibrillating stretched film, monofilament extrusion, bi-constituent monofilament extrusion, and the like. For example, in Japanese Pat. No. 9651/1960 there is disclosed a process wherein a mixed melt of at least two normally solid and incompatible thermoplastic resins (e.g., polystyrene and polyethylene) are extruded through the slit in a film-forming die to form a film which is next stretched and then cut into a plurality of filaments which are rectangular in cross-section. The resultant filaments are subsequently further cut into fibers which are then beaten mechanically as in a normal papermaking operation to fibrillize the cut (to lengths of about 0.3 to 2.5 cm) fibers. The resultant fibers and fibrillized fibers are each composed of the mixed resin composition, and are useful in the manufacture of the synthetic papers.
See also Japanese Pat. No. 5212/1964 wherein a mixed melt of like resins (e.g., powdered vinylidene chloride and low pressure polyethylene) is extruded as a monofilament, cooled and solidified, stretched, and beaten with a wooden hammer (without cutting the drawn filament), either as is or after being woven into a suitable fabric. Alternatively, the stretched fibers can be beaten after combing the same with an iron comb, crushed between conventional cylinders and then cracked into short fibers; or, in another embodiment, drawn and beaten by rubbing the fibers on the edge of a square, stainless steel bar.
The thus-obtained fibers have a length of several tens of millimeters and can also be fabricated into paper-like sheets, especially when screened in admixture with ordinary paper pulp. And in Japanese Pat. No. 6215/1966 a process is disclosed for extruding or spinning continuously a shaped filamentary structure of crystalline synthetic polymer comprising a three-dimensional integral plexus, by extruding a certain thermoplastic composition (e.g., a mixture of linear polyethylene and methylene chloride) through a suitable orifice under relatively high pressure and temperature into a zone of lower pressure.
However, these aforesaid methods of the prior art are not satisfactory for economical mass production because the resins employed are either highly incompatible with water or are relatively insoluble therein, and, in addition, in the performance of such methods complicated machinery and/or other highly sophisticated apparatus are required. Moreover, since the very hydrophilic cellulosics need not be employed in such processes, the synthetic papers fabricated from such thermoplastics do not necessarily exhibit those properties necessary in a desirable synthetic paper or similar sheetlike material.
It is of course well known that polyvinyl alcohol can be formed into fibers and filaments, but the most extensively used process to accomplish the above aims is quite complicated and involves the spinning of an aqueous solution of PVA, or solution of PVA in other suitable inert solvent. And such preparation of fibers and filaments of PVA depends essentially upon various physical changes that take place during the process.